The diffuser effect on free flow turbines shows a possibility of reaching a power coefficient greater than that of a classic turbine, exceeding the Betz limit. The present work evaluated the effect of an Eppler 423 profile diffuser coupled in a horizontal axis wind turbine with a 4-bladed rotor NACA 65(3) 618 profile. Using computational fluid mechanics (CFD, Computational Fluid Dynamics), numerical simulations were performed allowing to obtains more information about the fluid flow and the increase in extracted power for configurations with and without diffuser for the velocity of 7 m/s. Considering the dimensions of the test section, the results obtained
in the CFD analyses were validated through experimental results, in which the rotor and diffuser assembly were confined in a wind tunnel. It was observed that coupling the diffuser to the turbine considerably increased the fluid velocity, providing a 37% increase in the initial velocity of the flow. Showed an increase in the power coefficient in the order of 45,45% with the use of the diffuser, for the same flow velocity, 7 m/s. Thus, through the results obtained numerically in this work, it was possible to obtain reliable data for the evaluation of a specified Blade Element Momentum (BEM) model applied to diffuser-augmented wind turbines, which is employed to analyze the same turbine rotor and diffuser designs. Despite the good results of the BEM model, the present study indicates possible improvements for the consistency of the modeling.
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